Several genera covered on this site — Bertolonia and Sonerila especially — genuinely struggle in average home humidity, no matter how carefully they're watered. For these species, a closed or semi-closed terrarium isn't a decorative choice; it's often the difference between a plant that merely survives and one that actually thrives.

Choosing the right container

A glass container with a lid, or one that can be substantially closed, is the starting point — the enclosed environment is what maintains the high, stable humidity these genera need without constant manual misting. Size matters less than sealing quality; a smaller, well-sealed terrarium will maintain humidity more reliably than a large, loosely covered one.

Building the layers

  1. Drainage layer: a base of gravel or expanded clay pellets, keeping plant roots out of standing water at the bottom.
  2. Barrier layer: a thin layer of mesh or fine material preventing soil from washing down into the drainage layer over time.
  3. Growing medium: a light, well-draining mix similar to what's covered in our soil and fertilizer guide, adjusted slightly moister than a standard potted setup.
  4. Planting: low groundcover genera like Bertolonia or Sonerila work well toward the front and edges, with taller or trailing genera like Centradenia providing vertical interest further back.
A terrarium is a closed system — overwatering is a much bigger risk here than underwatering, since there's nowhere for excess moisture to actually go.

Ongoing maintenance

Once established, a well-built closed terrarium needs remarkably little intervention — occasional misting, periodic venting to prevent fungal issues, and light pruning to keep growth in check within the container's limited space. Bright, indirect light suits this setup well; direct sun through glass can overheat a closed terrarium quickly.

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